Semiconductor integrated circuit device

ABSTRACT

Using the leakage current of the base resistance of the bipolar transistor, semiconductor integrated circuit device which detects an overheat condition of the elements protected from overheat, is realized. The overheat detection circuit and the elements or the circuits which might be protected from overheat, are formed on the same substrate.  
     The said overheat detection circuit is comprised of a bipolar transistor, its base resistance, and a constant-voltage source. The constant-voltage source provides a certain voltage to isolate the elements.  
     The joint base resistance is located close to elements or circuits which might be protected from overheat and located far from the constant-voltage source.

FIELD OF THE INVENTION

[0001] The present invention relates to a semiconductor integratedcircuit device such as semiconductor integrated circuit device,especially relates to a semiconductor integrated circuit device on whichare mounted elements or circuits possibly to overheat and on which ismounted also an overheat detection circuit.

BACKGROUND OF THE INVENTION

[0002] As an overheat detection circuit mounted on the integratedcircuit, those circuits shown in the drawing FIG. 4A through FIG. 4Chave been known. In FIG. 4A, the circuit utilizes a thermalcharacteristic of diode's forward voltage drop, which detects thetemperature of a place where the diode is located, and the said circuitproduces an overheat detective signal when the temperature reaches acertain degree.

[0003] In FIG. 4B, an output is produced by the overheat detectivesignal in accordance with the increase of the leakage current of thebase opened transistor, i.e. the increase of the backward current of theparasite diode between the base and the emitter indicated by dottedline.

[0004] Furthermore, in FIG. 4C, the overheat detection circuit sensesthe temperature by using the thermal characteristic of theconstant-current source 1 and bipolar transistor 3 through the baseresistance 2, and at the same time amplifies the detection current.

[0005] For that reason, this circuit is designed to flow the outputcurrent of the constant-current source 1 from the joint of the base 3 ofthe transistor 3 and the base resistance 2 to the base resistance 2.

[0006] And the collector current of the bipolar transistor 3 istransformed into the voltage signal by the pull-up resistance 4 and thisvoltage signal goes through the buffer 5. Thus the overheat detectioncurrent might be produced. The base resistor 2 is usually formed by asemiconductor pattern and so forth, surrounded by the well region 2 awhich is clamped to the base 3 a of the transistor 3 in order to beisolated from the other circuit elements.

[0007] However, the above-said known overheat detection circuits usedfor the semiconductor device has advantages and disadvantages at thesame time. For example, both the circuit shown in FIG. 4A and thecircuit shown in FIG. 4C have an advantage and a disadvantage. It iseasy to define the temperature freely to produce the detective signal,but it is difficult to match the transition into the overheat conditionto what temperature of the detection.

[0008] As to the circuit in FIG. 4B, an advantage, on one hand, todetect correctly the transition into the overheat conditions since theleakage current changes rapidly in accordance with the overheatconditions. On the other hand, it is difficult to design a circuit toobtain the stable operation.

[0009] As the circuit in FIG. 4C has a base resistance, it is practicalto use the circuit and it has an advantage to utilize the currentamplification of the transistor without further additional elements.

[0010] In considering the above-said problem, such an overheat detectioncircuit is requested as can detect correctly the transition into theoverheat condition and is easy to utilize. In replying to the request,one idea is to make react to the leakage current as in FIG. 4B,maintaining the advantage of the overheat detection circuit as in FIG.4C. Therefore, it is the technical problem to improve the detectioncircuit based on the circuit in FIG. 4C.

SUMMARY OF THE INVENTION

[0011] It is an object of the invention to realize the semiconductorintegrated circuit device which detects the overheat by way of theleakage current of the base resistance of the transistor The abovementioned object of the present is accomplished by using the leakagecurrent of the base resistance of the bipolar transistor. It is anobject of our invention to realize a semiconductor integrated circuitdevice which detects an overheat condition of the elements protectedfrom an overheat is realized. That is, the overheat detection circuit isformed on the same substrate where the elements or the circuits whichare protected from overheat are formed. The said overheat detectioncircuit comprises a bipolar transistor, its base resistance, and aconstant-voltage source. The said constant-voltage source provides acertain voltage necessary to isolate the elements. In comparison withthe prior art, overheat detection circuit in FIG. 4C, a constant-voltagesource is introduced, and the base resistance is clamped to the outputof the constant-voltage source.

[0012] In this semiconductor integrated circuit device, the leakagecurrent from the well region to the base resistance is detected. Theleakage current is stabilized by the constant-voltage source and isamplified by the transistor. And the operation of the bipolar transistoris stabilized because of the base resistance.

[0013] According to this invention, a semiconductor integrated circuitdevice, which detects an overheat based on the leakage current of thebase resistance of the transistor, will be realized.

[0014] Another improvement is that in the above-mentioned device, thebase resistance is located close to an elements and circuits protectedfrom the overheat and located far from the constant-voltage source.

[0015] In this way the temperature of an object protected from overheatcan be detected correctly based on the leakage current of the baseresistance.

[0016] As the constant-voltage source which provide a certain voltagewith the well region is located far from the protected objects, theconstant-voltage source is not influenced by the thermal change causedby the overheat protected elements or circuits.

[0017] A certain voltage which contributes to a stabilization of theleakage current, is not influenced by the undesired thermal change.Therefore an overheat detection can be made correctly.

[0018] According to this second invention, a semiconductor integratedcircuit device which can detect the overheat correctly based on theleakage current of the base resistance of the transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is one of the embodiment of this invention, FIG. 1A being acircuit of the overheat detection circuit, and FIG. 1B being a frontview in longitudinal section, showing the overheat detection circuit ofthis invention;

[0020]FIG. 2 is a circuit of the whole device of this invention;

[0021]FIG. 3 is a drawing which describes the detection operation;

[0022]FIG. 4A through FIG. 4C are drawings showing a prior art overheatdetection circuit.

PREFERRED EMBODIMENT OF THE INVENTION

[0023] Now, an embodiment of the present invention will described withreference to drawings. FIG. 1 shows the fundamental structure, FIG. 1Abeing the overheat detection circuit, FIG. 1B being the longitudinalcross section of the region where the base resistance is formed. FIG. 2is the whole circuit of the device. The same number is used for theelements identical or relevant to those in the said prior art circuits.

[0024] This semiconductor integrated circuit device (in FIG. 2) has anone-chip-substrate 10. On this substrate an overheat detection circuit(2-6), an output-transistor 9 which is protected from the overheatcondition and a control circuit 8 which controls output transistor 9 inaccordance with the result of the overheat detection.

[0025] As two sets of the output transistor 9 and control circuits aremounted on the substrate, a detective signal distribution circuit 7 isprovided in order to transmit overheat detective signal to both of thecontrol circuits 8.

[0026] The overheat detection circuit (2-6) (in FIG. 1A) is providedwith the NPN transistor 3. The base resistance 2 is connected to thebase of the transistor as an overheat detection element which usesleakage current. In order to use it in the grounded-emitter connectionmode which is practical to use, the transistor 3 is designed so that thebase 3 a of which is connected through the base resistance 2 to theground GND, the emitter of which is connected to the ground GND, thecollector of which is connected through pull-up resistor 4 to the powersupply line Vcc. In addition, in order to produce the detective signal,the heat detection circuit (2-6) consists of the said pull-up resistance4 which transforms the collector current into the voltage and of thebuffer 5 having MOS transistor which may switch in accordance with thevoltage.

[0027] In order to form the base resistance 2 in the overheat detectioncircuit (FIG. 1B), in case the substrate 10 is p-type, firstly n-typewell region 2 a should be formed and then p-type spot having anappropriate density is formed in an appropriate width and length withinthe said region 2 a, so that the desired resistance and thermalcharacteristic are obtained.

[0028] The well region 2 a is connected to the constant-voltage source6, in order to isolate the base resistance 2 from other elements andcircuits and in order to supply the leakage current in a stablecondition. Thus a certain voltage, which is higher than the base mayreach, is supplied to the well region 2 a. The joint between theconstant-voltage source 6 and the well region 2 a, is made closer to thenode of the base 3 a and base 2 than the node of ground GND and baseresistance 2 so that most of the leakage current runs toward transistor3. In addition, high precision band-gap-voltage source and so forth issuitable for the constant-voltage source 6, and other type voltagesource may also be used.

[0029] The output transistor 9 and the control circuit 8 (FIG. 2)constitute a power source which supplies power of a certain voltage toan external load. In that case the output transistor 9 is, for example,comprised of power elements such as MOS transistor. And the controlcircuit 8 controls on-off switching operation of the transistor 9 or itsanalog operation in accordance with the external input indicated and thefeedback signal not indicated.

[0030] Also this circuit 8 stops the transistor 9's operation onreceiving the overheat detective signal through the detective signaldistribution circuit 7 from the buffer 5.

[0031] The said distribution circuit 7 may be comprised of MOStransistors or of bipolar type elements and some other elements insofaras it transmits the buffer's output to the control circuit 8, matchingthe output of the buffer 5 to the input of the control circuit 8.

[0032] Referring to the layout of the semiconductor integrated circuitdevice, the base resistor 2 and the bipolar transistor 3 may be locatedclose to each other, preferably in the middle of them. And theconstant-voltage supply source 6, the pull-up resistance 4 and thebuffer 5 may be located as far as possible from the output transistor 9in order to avoid the influence of the heat produced by the transistor9.

[0033] The mode and operation of the above said semiconductor integratedcircuit device will be described referring to the figures. FIG. 3describes the detection operation, especially describes the leakagecurrent in the overheat detection operation and the collector currentwhich amplifies the said leakage current.

[0034] In the normal operation mode, the current running in the baseresistance 2 which are made up of forward current and leakage current,are very small, so that the transistor 3 is off. As a result thedetective signal that is transmitted to the control circuit 8 throughthe buffer 5 and the detective signal distribution circuit 7, is notsignificant, i.e. the detective signal does not affect the operation, orthe said detective signal is not transmitted.

[0035] The external input signal controls the operation of the circuit8. Therefore the control circuit 8 controls the output transistor 9 inaccordance with the external input signal, so that the transistor 9keeps the switching operation.

[0036] The temperature of the transistor 9 rises as the transistor 9operates, and so does the temperature of the base resistance region 2.

[0037] And so does increase the leakage current running through wellregion 2 a and base resistance 2 from the constant-voltage source 6 tothe ground GRD and to the base 3 a of the transistor 3(2 dotted line inFIG. 3)

[0038] The leakage current which is run to the base 3 a is amplified bythe factor hfe(current amplification), and transformed into thecollector current.

[0039] As the leakage current of the base resistance 2 made fromsemiconductor increases rapidly when the temperature of thesemiconductor device approaches to the limit of operation, thetemperature of the transistor 9 approaches to the upper limit, asignificant detective signal is transmitted through the pull-upresistance 4 and the buffer 5.

[0040] And the control circuit 8 forces the transistor 9 to stop theoperation.

[0041] Thus when the output transistor 9 becomes overheated, thedetection circuit(2-6) detects it and stops the operation of thetransistor 9.

[0042] The stop continues until the temperature of the transistor 9 goesdown. When the temperature goes down to the certain degree, thetransmission of the significant detective signal from the overheatdetection circuit(2-6) stops and the operation of the transistorreopens.

[0043] In addition to the accurate detection of the overheat condition,in the normal operation mode when the circuit does not detect theoverheat condition, the transistor 3 operates in a stable way since thebase 3 a of the transistor 3 is grounded through the base resistance 2.So the malfunction caused by instantaneous change of power supply lineVcc and electromagnetic noises coming from the exterior may be avoided.As a result, undesirable cases do not occur where the normal operationis stopped by the transmission of the unfavorable detective signal

[0044] In the above said cases, the circuit has 2 output transistors 9which are protected from an overheat. It may have one or more than threetransistors.

[0045] And plural overheat detection circuits (2-6) may be used.

[0046] Moreover, transistor 3 may be PNP, not limited to the NPNtransistor. Also, substrate 10 may be n-type, not limited to be p-type.

[0047] As for the p-type substrate 10, firstly p-type well region 2 ashould be formed and within that region 2 a n-type base resistance 2 ofappropriate density should be formed. The buffer 5 and the outputtransistor 9 may be bipolar transistor or may be some other sort of theelements, not limited by the MOS transistor. And the circuit may consistof a plural elements, not limited by a sole element.

[0048] It is clear from the above description that in the firstembodiment, by changing the clamp point of the well region of the baseresistance to the constant-voltage source, semiconductor integratedcircuit device is realized, that can detect overheat based on theleakage current of the base resistance of the transistor.

[0049] Moreover, in the second embodiment, by allocating the overheatdetection circuit in the semiconductor integrated circuit device, theoverheat detection circuit semiconductor integrated circuit device isrealized, that can detect more accurately overheat, based on the leakagecurrent of the base resistance of the transistor.

What is claimed is:
 1. A semiconductor integrated circuit devicecomprising: an overheat detection circuit formed on the same substratewhere the elements or the circuits which are protected from an overheatare formed, the said overheat detection circuit comprising bipolartransistor, its base resistance, and a constant-voltage source whichprovides a certain voltage to the well region where is formed the saidresistance.
 2. A semiconductor integrated circuit device as define inclaim 1, where the said base resistance is located close to the saidoverheat protected elements or circuits as well as the constant-voltagesource, and at the same time the said base resistance is located farfrom the said overheat protected elements or circuits.